The invention concerns a distraction system for long bones with an intramedullary pin, which has a wall bounding a hollow space, with a distal end and a proximal drive-in end, and with a guide socket enclosing the proximal drive-in end of the intramedullary pin in the sliding seat, whereby the intramedullary pin has an inner part arranged in a longitudinally displaceable manner in the hollow space, in which a coaxial borehole with an internal thread is extended proceeding from its front side turned toward the proximal drive-in end, an abutment provided in the hollow space at a distance from the drive-in end, a rod having an outer thread, which engages as a screw with the inner thread of the borehole of the inner part, and which is coupled to a rotating drive lying on the abutment and arranged inside the hollow space, attachment holes for passage of distal attachment bolts arranged at a distance passing through the wall crosswise in the region of its distal end, a distal longitudinal hole [or holes] parallel to the longitudinal extension of the intramedullary pin arranged distally to the abutment and passing crosswise through the wall bounding the hollow space, if necessary on opposite-lying sides, and at least one attachment hole aligned flush with the longitudinal hole in the wall bounding the hollow space and passing crosswise through the inner part for passage a proximal attachment bolt.
The intramedullary pin utilized in this arrangement is known from EP 0 432,253 A1 and DE 3,921,972 C2. Bone elongations and segmental dislocations are possible according to the callus distraction method with this intramedullary pin. By application of integrated drives, the entire intramedullary pin can be implanted and can operate without material connection to the outside, which considerably reduces the risk of infection. As a rule, two longitudinal holes lying opposite one another or attachment holes lying opposite each other in pairs are provided in the wall of the intramedullary pin. With the use of intramedullary pins with wall open in their longitudinal direction, however, one longitudinal attachment hole or one attachment hole in the wall can suffice, since the wall is open on the opposite-lying side. Elongations of the femur of up to 10 cm also in combination with axial corrections can be successfully conducted with the intramedullary pin in the above-described configuration.
Indications for segmental dislocations exist when large bone defects are present of approximately 2 to 3 cm and more, such as may arise, e.g., directly as primary bone loss after impact situations, but also as secondary bone loss following infection or necrosis. Further, successful operations in the case of malignant bone tumors leave behind large bone defects.
If the known intramedullary pin is applied to segmental dislocation, an additional locking of the primary proximal fragment must be provided, so that the leg does not twist or become shortened. Frequently, the situation also exists where a shortening has already occurred, so that the defect may in fact be bridged with the segmental dislocation, but in addition to the segmental dislocation, another elongation of the extremity associated with this is also necessary.
In order to separately secure the proximal bone segment against axial dislocation in the case of a segmental dislocation, U-shaped notches are formed in the intramedullary pin according to DE 3,921,972 C2 in the region of its proximal end, and the legs of the U run parallel to the axis and the bottom combining segments are turned toward the drive-in end. Lamellae are formed by the U-shaped notches. A socket-shaped wedge element with outer wedges is guided in the proximal end of the intramedullary pin, and this element is axially displaced by rotating a screw held in threaded engagement by insertion at the drive-in end, and spreads apart the lamellae into a wedged position by its outer wedges, whereby a form fit with the proximal long bone and thus its secure positioning is achieved.
This design serves for the axial and rotational stabilization of the primary proximal bone fragment, as is necessary for segmental dislocation. A segmental dislocation in combination with an elongation, however, is not possible with this configuration. In addition, the later removal of the intramedullary pin is made difficult due to the spreading apart of the lamellae.
It has further been shown that a growing together of the dislocated segment and the primary fragment at the place of contact, which is also designated the docking site, is problematical at the end of segmental dislocation. The relatively reaction-poor front surfaces also have the tendency to bridge over under compression, so that for the most part additional compressive osteosyntheses or even an operative intervention and the addition of cancellous bone, for the most part from the pelvic crest, become necessary.
The arrangement of a guiding socket in the sliding seat around the proximal drive-in end of the intramedullary pin is already known from the literature citation Baumgart R., Betz A., Kettler M., Zeiler C., Schweiberer L.: Perspectives of Callus Distraction, Unfallchirurg 99, 84-91, 1996 [in German]. The objective of the arrangement of the guide socket primarily consists of a stabilizing effect, if the intramedullary pin migrates far into the bone at the end of treatment, since in this position, high tension peaks would otherwise be expected at its proximal end. The greater trochanter is inserted into the proximal force uptake component with the guide socket, whereby the danger of a loosening of the intramedullary pin or a proximal fracture of the femur is reduced.
The guide socket also essentially contributes to the simplification of the removal of the intramedullary pin, since in the case of intramedullary pins that have penetrated far into the medullary space, at the end of the distraction in the case of large elongation segments, the finding of the end of the intramedullary pin and the placement of the extraction instruments may present difficulties.
The guide socket itself is held laterally in the greater trochanter by means of an overlaying strap with an opening, through which the attachment means to the long bone, for example, a screw, can be introduced, so that the position of the guide sleeve is secured both axially as well as in a rotational manner. The axial securing against displacement is necessary in any case, because both a sliding distally into the medullary space, as well as particularly a sliding out proximally from the medullary space represent disadvantages and lead to a loss of function.
The use of such a distraction system is limited to elongations of the long bone; segmental dislocations and combinations of segmental dislocations and elongations cannot be conducted.
An intramedullary pin is known from DE 195-27,822 C1 for the rigid combining of parts of a bone. The intramedullary pin has a sheath that can be attached to one bone part and a rotatable socket can be taken up in this sheath. The rotatable socket can be joined with another bone part by means of a longitudinal guide introduced into the sheath. The rotatable socket engages in form-fitting manner on a threaded spindle. The threaded spindle is joined with a transport element, which can be connected with another bone segment arranged between two bone parts that is separated from a fracture end. The transport element can be moved in translation along the longitudinal axis in the sheath by rotating the rotatable socket. The attachment of the bone segment separated from one fracture end is made by means of a bone screw, which is guided in the sheath by means of a longitudinal guide. The two bone parts are thus joined with the sheath by means of bone screws and are joined in the pre-given operative position. This means that the shortened bone can be stabilized only intraoperatively in the original length. The structure of the intramedullary pin permits limited radial angular movements of the distal bone part, which are converted into an axial movement of the transport element by means of a toothed gearing with directional blocking and the threaded spindle, and this motion in turn displaces the bone segment in the defect between the bone parts. Only a segmental dislocation can be achieved with the known intramedullary pin. A bone elongation as well as a combination of segmental dislocation and elongation according to the callus distraction method is not possible.